A tripod turnstile gate, also called a baffle gate, is a form of
gate which allows one person to pass at a time. It can also be made
so as to enforce one-way traffic of people, and in addition, it can
restrict passage only to people who insert a coin, a ticket, a
pass, or similar. Thus a turnstile can be used in the case of paid
access (sometimes called a faregate when used for this purpose),
for example public transport as a ticket barrier or a pay toilet,
or to restrict access to authorized people, for example in the
lobby of an office building.

From a business/revenue standpoint, turnstiles give an accurate,
verifiable count of attendance. From a security standpoint, they
lead patrons to enter single-file, so security personnel have a
clear view of each patron. This enables security to efficiently
isolate potential trouble or to confiscate any prohibited
materials. They can, on the other hand, become a serious safety
issue when a speedy evacuation is needed.